1. Field of the Invention
The present invention relates to an inductive load controlling device used in a linear solenoid actuator that can be applied to automatic transmission for vehicles.
2. Description of the Related Art
One of conventional electric current control methods for the current in a linear solenoid that is used for an automatic transmission for vehicles controls the current in an inductive load by pulse width modulation (PWM) control.
FIG. 10 is a block diagram showing an example of outline structure of a closed loop control system to be applied to a conventional inductive load driving controller.
As shown in FIG. 10, to an end of an inductive load 105, which can be a linear solenoid, a driving circuit 103 for driving the inductive load 105 is connected and to the other end of the inductive load 105, a current detecting resistance 107 is connected in series. At the preceding stage of the driving circuit 103, a drive controlling circuit 102 is connected to perform PWM control in an analogue process. At the preceding stage of the drive controlling circuit 102, a D/A converter 101 is connected.
An average current detecting circuit 104 is connected to the both ends of the current detecting resistance 107 to detect an average value of electric current through the inductive load 105. The output terminal of the average current detecting circuit 104 is connected to the drive controlling circuit 102.
Current value controlling information FC indicating target current value through the inductive load 105 is converted to an analogue data in the D/A converter 101, and then delivered to the drive controlling circuit 102. Current If running in the inductance L of the inductive load 105 flows through the current detecting resistance 107. The average current detecting circuit 104 detects the average value lavr of a load current If through the inductive load 105 and delivers the lavr to the drive controlling circuit 102.
The drive control circuit 102 generates a PWM signal so that the average value lavr of the current If through the inductive load 105 equals the target value indicated by the current value controlling information FC, and thus PWM controls the current If flowing through the inductive load 105 by ON/OFF controlling switching elements in the driving circuit 103.
FIG. 11 is a block diagram of another example of schematic construction of a closed loop control system to which a conventional inductive load drive controlling device is applied.
As shown in FIG. 11, to an end of an inductive load 105, a driving circuit 103 is connected and to the other end of the inductive load 105, a current detecting resistance 107 is connected in series. At the preceding stage of the driving circuit 103, a drive controlling circuit 112 is connected to perform PWM control in a digital process.
An average current detecting circuit 114 is connected to the both ends of the current detecting resistance 107, and the output terminal of the average current detecting circuit 114 is connected to the drive controlling circuit 112 through an ND converter 111.
The drive controlling circuit 112 receives a current value controlling information FC indicating a target value of current flowing in the inductive load 105. Electric current If running in inductance L of the inductive load 105 flows through the current detecting resistance 107, and an average value lavr of the current If running in the inductive load 105 is detected by the average current detecting circuit 114. The average value lavr is converted to a digital data in the A/D converter 111 and then delivered to the drive controlling circuit 112.
The drive controlling circuit 112 generates a PWM signal to perform PID control so that the average value lavr of the load current If running in the inductive load 105 is equal to the target value indicated by the current value controlling information FC, and thus PWM-controls the current If running through the inductive load 105 by ON/OFF-controlling switching elements in the driving circuit 103.
FIG. 12 is a timing chart showing schematically the waveform of the current If through the inductive load 105 in the process of PWM-control by a conventional inductive load drive controlling device.
As shown in FIG. 12, the current If through the inductive load 105 increases during the PWM signal is at a high level and decreases during the PWM signal is at a low level. The current If is so controlled that the average value lavr of the current If equals the target value indicated by the current value controlling information FC.
The state of the PWM signal (a high level or low level) depends on the function of the switching elements used in the driving circuit 103. In the example described above, the switching elements are assumed to turns on at a high level of the PWM signal and turns OFF at a low level of the PWM signal.
FIG. 13 is a block diagram of an example of construction of a hydraulic transmission device for vehicles in which a conventional inductive load controlling device is installed.
As shown in FIG. 13, whole the transmission device is controlled by an electronic control unit 122 that includes drive controlling devices each comprising a driving and controlling circuit 124 for directly controlling a linear solenoid 121, in turn driving a hydraulic pressure control device 120 and a microcomputer 123 for controlling the driving and controlling circuits 124.
Japanese Unexamined Patent Application Publication No. 2010-242806 discloses a linear solenoid module that comprises; an interface circuit for receiving a current command value for a solenoid actuator, a characteristic parameter memory element for storing correction characteristic parameters to obtain a uniform characteristic in the solenoid actuator, pulse width modulation (PWM) control circuit, a driving circuit, a current detecting resistance for detecting the load current in the solenoid actuator, and a linear solenoid controlling circuit having an average current detecting circuit and a temperature sensor.
Japanese Patent No. 3622436 discloses a solenoid controlling device for controlling a hydraulic pressure control circuit having a solenoid of a vehicle behavior controlling device. The solenoid control device comprises a relaxation processing means for relaxing a target current value corresponding to a status of the vehicle and an electric signal setting means for setting an electric signal to control the solenoid based on the deviation of the current actually flowing in the solenoid from the target current value that has been subjected to the relaxation processing.
Japanese Patent No. 3205444 discloses a solenoid driving device of an automatic transmission, the solenoid driving device having a means for detecting an oil temperature of the automatic transmission and a predetermined map, and controlling a rising characteristic of the solenoid based on both the actual oil temperature of the automatic transmission and the oil temperature inside the solenoid.
Japanese Unexamined Patent Application Publication No. H07-077271 discloses a hydraulic pressure control device of an automatic transmission comprising: a means for making a control parameter overshoot temporarily beyond a target command value when the target value to the solenoid is changed and then making the parameter return to the target command value, a means for detecting oil temperature, and a means for determining a degree of the overshooting corresponding to the detected oil temperature.
In the conventional example of FIG. 13, to drive-control the linear solenoid installed in a hydraulic transmission for vehicles, whole the transmission device is controlled by an electronic control unit 122 that includes drive controlling devices each comprising a driving circuit for directly controlling a linear solenoid and a drive controlling circuit for controlling this driving circuit. Since the linear solenoid installed in the transmission has a temperature dependent characteristic, it is necessary, in the process of developing a drive control device, to define a parameter for temperature correction in the control program in the microcomputer installed in the electronic control unit 122. The defined parameter needs to be adjusted in the process of manufacturing the transmission to set an optimum parameter for each transmission device.
Concerning this parameter setting, the conventional example disclosed in Japanese Unexamined Patent Application Publication No. 2010-242806 comprises, in the linear solenoid module, an information memory section for storing correction characteristic information to obtain a uniform characteristic and a control circuit for carrying out correction processing based on the correction characteristic information stored in the information memory section. Thus, characteristic correction processing can be performed in the linear solenoid module itself to simplify the parameter adjustment.
Automatic transmission for vehicles, however, needs to meet the demands: that overshoot, undershoot, or ringing does not occur with respect to the target current value, which is referred to as a requirement 1, and that fast responsiveness is necessary to reach the target current value in a short time, which is referred to as a requirement 2.
In the inductive load drive controlling device shown in FIG. 11, the requirement 2 can be met by conducting tuning of a differential control (D control) of the PID compensation control. On the other hand, the requirement 1 is hardly satisfied. Thus, the requirement 1 and the requirement 2 are in a trade-off relationship.
The conventional example disclosed in Japanese Patent No. 3622436 can satisfy the requirement 1 owing to a control device that is additionally provided with a filter for relaxation processing. However, optimum control for the requirement 2 cannot be performed because the relaxation processing essentially takes certain time to reach a target current value.
The conventional examples disclosed in Japanese Patent No. 3205444 and Japanese Unexamined Patent Application Publication No. H07-077271, which perform control with temporary overshoot with respect to the target current value, take into account the oil temperature of the automatic transmission and the oil temperature in the solenoid, and give an amount of overshooting by giving a fixed magnitude of current I and time T irrespective of the changed quantity in the target current value. Thus, optimum control for the requirement 2 cannot be performed.